Our group has developed powerful techniques for studying singlet oxygen and some other strong oxidants. These include laser flash spectroscopy, detection of singlet oxygen phosphorescene, kinetic methods of characterizing reactive species and reaction mechanisms, low-temperature detection of unstable primary reaction products, and specific trapping agents that may be used even with living systems. We will use these techniques described above and develop new, more specific ones for study of photodynamic sensitizers and the mechanisms by which they damage organic molecules, and of reactions of oxygen species with biological target molecules. The production of singlet oxygen by important natural photosensitizers and their ability to undergo competing reactions will be determined. New photodynamic sensitizers for phototherapy that are chemically pure and absorb strongly at useful wavelengths will be prepared and their singlet oxygen yield determined. The rates and primary products of attack of singlet oxygen on important biological molecules such as guanosine and ascorbate will be determined. Some of the products are models for intermediates in enzymatic processes, and their preparation by non-photochemical routes will be attempted. Activation parameters for the reactions of carotenes and phenols will be measured to help determine the mechanisms by which they deactivate singlet oxygen. Possible electron transfer processes by some of these substrates will be investigated. The yield of singlet oxygen from some oxidative reactions of superoxide ion will be determined. Environmental influences on superoxide dismutation and its nucleophilic reactivity will be studied, and new chemical trapping agents for it will be prepared and characterized.